Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention relates to a method for preparing alkyltin trihalides.
This invention further relates to an improved method for preparing alkyltin
trihalides by the catalyzed reactlon between a stannous halide and an alkyl
halide. ~
United States Patent 3,340,283 whichissued May 9, 1967 to Gloskey -
discloses preparing organotin trihalides, RSnX3, wherein X represents
chlorine, bromine or iodine, by reacting a stannous halide, SnX2, with the
corresponding hydrocarbon halide, RX. The reaction is carried out under
autogenous pressure and in the presence of an amine catalyst. The desired
organotin trihalide is isolated using conventional techniques, which include
selective extraction and distillation. The process as disclosed in the
aforementioned patent makes no provision for recovery and recycling of the
catalyst, which may represent a significant economic investment, particularly
for a commercial scale process employing relatively large amounts of cata-
lysts for a single reaction. In addition, the catalyst may be present as -
; a complex that contains as much` as 6% by weight of organotin compounds,
including the desired product. These complexes are relatively stable under
the condltions employed to prepare and isolate the organotin trihalide.
These complexes can reportedly be decomposed by the addition of water. While
hydrolysis of the complex could result in higher yields of the organotin
trihalide, it may also introduce undesirable water-soluble impurities into
the organotin product, including antimony and iron compounds. This is
particularly true for the
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water-soluble organotin trihalides such as methyltin trichloride and
butyltin trichloride. In addition, some end uses require that the water
employed to decompose the complex be removed by distillation or other
suitable means. This separation step significantly increases processing
costs.
United States Patent 3,519,667 whichissue~July 7, 1970 to Molt
et al describes the preparation of alkyltin trichlorides by the reaction
between stannous chloride and either methyl chloride or ethyl chloride.
The reaction is preferably conducted under atmospheric pressure and in the
presence of a phosphonium chloride or a thiocyanate catalyst. The con-
centration of catalyst required is between 0.4 and 0.7 mole per mole of
stannous chloride. This relatively high catalyst concentration appears
necessary to achieve a useful reaction rate under atmospheric pressure.
Whatever the reason may be, the large amount of catalyst required signifi-
cantly reduces volume efficiency and increases production costs.
~ ne objective of this invention is to reduce the concentration
of catalyst required to prepare alkyltin trihalides. A second objective
is to more effectively utilize the catalyst together with any organotin
compounds that may have complexed with the catalyst in the reaction mix-
ture. Surprisingly it has now been found that yield and volume efficacycan be increased and the amount of catalyst reduced if the reaction be-
tween a stannous halide and a lower alkyl halide is carried out under a
pressure of between 50 and about 500 p.s.i. (3500 and about 35,000 g./cm.2)
and in the presence of a diluent consisting at least in part of the
catalyst-containing residue from a previous distillation of a lower alkyltin
trihalide prepared in accordance with the present method.
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This invention provides in an improved method for preparing
an alkyltin trihalide, wherein the alkyl group contains between one and
five carbon atoms and the halogen, represented by X, is chlorine, bromine
or~iodine, by reacting the corresponding alkyl halide, RX, with a stannous
halide SnX2 at a temperature of between 150 and 250C., and isolating the
resultant alkyltin trihalide by distillation, the reaction between said
alkyl halide and stannous halide being conducted in the presence of a
diluent and a catalyst selected from the group consisting of amines and
. phosphines of the general formulaeR3N and R3P, respectively, and the onium
salts of said amines and phosphines wherein each Rl is individually select-
ed from the group consisting of hydrogen atoms and alkyl radicals containing ~ .
between 1 and 20 carbon atoms, cycloalkyl, aryl, alkaryl and aralkyl radicals
wherein the alkyl residue of said alkaryl or aralkyl radical contains between
1 and 20 carbon atoms, the improvement which resides in
(a) conducting said reaction under a pressure of between
50 and 500 p.s.i. and in the presence of a diluent consisting, at least in
part, of the residue remaining following a previous distillation for the
recovery of said alkyltin trihalide, said diluent being a solvent or
dispersant for the catalyst and a solvent for the alkyltin trihalide,
and
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Ib) maintaining the catalyst concentration in
¦said ~esidue at between 0.005 and about 0.15
mole of catalyst per gram at~m of tin present
¦in the reaction mixture.
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DETAILED DESCRIPTION OF THE INVENTION
¦ The present method for preparing lower alkyltin
¦ trihalides employs Iess catalyst than heretobefore
disciosed in the prior art and, more importantly, I
improves product yield by recycling the catalyst, thereby . .
utilizing the organotin compounds which are complexed with
the catalyst.
The aforementioned U. S. Patent 3,519,667 teaches
using 1 mole of catalyst for every two moles of stannous
halide, since the amount o~ stannous chloride converted to
organotin trichloride is allegedly never greater than the
amount of catalyst, on a molar basis. The disclosure contained
:~ ln this patent indicates that the reaction between stannous
chloride and methyl chloride can be conducted at higher than
. atmospheric pressures using less catalyst than required at
atmospheric pressure due to the higher concentration of methyl
chlorlde present, in the liquid phase. Since stannous chloride
does not have a significant vapor pressure under the ~ ' .
. ,~onditions o~ the reaction, only the methyl chloride
: dissolved in the liquid phase would be expected to react.
In accordance with Henry's law, there 1s a linear
relationship between the concentration o~ methyl chloride in
, the solution and the partial pressure of this gas. Henry's
., law can pe expressed as P=kX where P represents the pressure
of the gas, X the mole ~raction of the gas present in the
25 ' solvent, which in the present invention is the reaction medium
containing the stannous halide, and k is an experimentally
¦¦ determine constant, whlch for most gasses has a value Or
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between 10 and 10 . Assuming that methyl chloride or
I other alkyl halide exists as a gas under the conditions of the
¦ present reaction and obeys Henry's law, if the pressure were
¦ increased to ten times atmospheric pressure, the concentration
¦ of the gas in solution would be expected to be ten times the
value at atmospheric pressure. The amount of catalyst required
I to provide an equivalent reaction rate at the higher pressure
; ¦ should there~ore be proportionately lower. Specifically, a
¦ 10 fold increase in pressure should allow about a 10 fold
10 ¦ decrease ln catalyst concentration without affecting the
reaction rate to any significant extent. Surprisingly the
¦ present method employs between 0.005 and 0.15 mole of catalyst,
preferably less than 0.05 mole of catalyst per gram atom of
tin present in the reactlon mixture under pressures khat are
between 3 and 20 times atmospheric. In accordance with prior
art teachings, one would expect to employ more than 0~025 mole
of catalyst.
m e catalysts of the present invention are ammonia,
primary, secondary and tertiary amines, phosphines and onium
salts of these compounds. The amines and phosphines are of
the general formula R3N and R3P, respectively, wherein each
R is a hydrogen atom or a hydrocarbon radical, as previously
defined. Preferably the three R radicals are identical.
i~ Typical primary amines which can be employed in the
practice of this invention include: methyl amine, ethyl ',
amine, n-propyl amine, n-butyl amine, i-butyl amine, n-amyl
amine, hexyl amine, octyl amine, allyl amine, cyclohexyl amine,
benzyl amine, p-toluidine, aniline, p-methyl aniline,
~-pheny hyl-amine, ethylene diamine and p-ch~oro aniline.
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The secondary amines include dimethyl amine, diethyl amine,
di-n-butyl amine, di-n-amyl amine, dihexyl amine, dioctyl amine, diallyl -
amine, dicyclohexyl amine, dibenzyl amine, N-methyl ethyl amine, N-methyl
aniline, N-ethyl aniline, hexamethylene tetramine and N-methyl naphthyl-
amine.
Useful tertiary amines include trimethyl amine, triethyl amine,
tri-n-propyl amine,tri-n-butyl amine, trihexyl amine, triallyl amine and
tricyclohexyl amine.
Other amines include aniline, p-toluidine, o-toluidine, m-toluidine,
benzyl amine, pyridine, 2-methyl pyridine, 3-methyl pyridine, 2-ethyl
pyridine, 3-ethyl pyridine, quinoline, 6-methoxy quinoline, ~-picoline,
~picoline and gamma picoline. '
Inertly substitutedamines such as p-chloro aniline can also be
employed.
The phosphines corresponding to each of the foregoing amines can
also be used as catalysts for the present methot. Preferred catalysts
include trimethylamine, tributylamine, tributylphosphine and triphenyl-
phosphine.
In the presence of the alkyl halide all of the catalysts,
including ammonia and phosphine, are converted to the corresponding
quaternary ammonium halide or phosphonium halide. If desired, the
catalyst can be added to the reaction mixture as the corresponding
quaternary onium salt, RlR ZX, wherein R is selected from the same group
as Rl, X is a monovalent anionic radical, preferably chlorine, bromine or
iodine and Z is nitrogen or phosphorus. Inorganic ammonium salts such as
ammonium chloride are also suitable. Other useful onium type catalysts
are disclosed in United States Patent 3,415,857 which issued October 12, 1968
to Hoye.
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The reaction between the stannous halide and alkyl
halide is conducted in the presence of a diluent that conslsts,
at least in part, of the residue from a previous distillation
of alkyltin trihalide prepared in accordance with the present
method and which contains an effective amount of one of the
present catalysts. Since the boiling points of the present
catalysts in the form of their onium salts are considerably
higher than that of the desired monoalkyltin trihalide,
substantially all o-f the catalyst employed for the reaction
is contained ln the residue, and can be recycled virtually
indefinitely. In many instances the residue is an adequate
diluent in which to carry out the reaction between the
stannous halide and alkyl halide. Should additional diluent
be required, for example, to reduce the viscosity of the
reaction mixture, one can employ any inert organic solvent.
Typical solvents include ethers such as diethylene glycol
dimethyl ether, diethyl ether, dibutyl ether, tetrahydrofuran
and aliphatic hydrocarbons, such as hexane, heptane, octane,
cyclohexane and those mixtures of hydrocarbons available as
mlneral oils, liquid paraffins or petroleum ethers. Preferably
the diluent consists, at least in part, of an alkyltin tri-
halide, usually the one to be prepared using the present method.
The diluent should be a solvent or dispersant for the
reactants and a solvent for both the alkyltin trihalide product
and the catalyst. The relative volumes of diluent and reactant
will vary somewhat depending upon process conditions. The
volume of diluent should always be sufficient to completely ?
disperse or dissolve the reactants and provide a fluid reaction
medium t tùe ~emperature o~ the reactlon, whlch 1s ~etween
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150 and 250C., pre~erably between 170 and 200C. The mixture
¦ should be sufficiently fluid to permit trans~erral of the
¦ reaction mixture to a distillation apparatus for recovery of
¦ the alkyltin trihalide from the reaction mixture.
m e distillation residue employed as the diluent
preferably contains between 0.005 and 0.15 mole of catalyst
per mole o~ stannous halide to be reacted and more than 0.5
mole of organotin trihalide per mole of catalyst. If less
than the required concentration of organotin trihalide is
present, the volume of diluent should be increased by the
addition of an inert organic liquid or additional alkyltin
trihalide as previously defined, until the volume of diluent
ls at least equal to the combined volumes of the stannic halide
and alkyl halide.
The alkyl halide and stannous halide are reacted
under a pressure of between 50 and 300 p.s.i. The pressure
is controlled by ad~usting the rate at which the alkyl halide
i8 added to the reaction vessel containing a stannous halide
and a diluent as descrlbed hereinbefore. Under the conditions
of the present method the reaction is substantially complete
,~ in from about 4 to 10 hours. Longer times may be desirable
to ensure substantially complete conversion, particvlarly in
large commercial scale reactors. me resultant mixture is
then distilled under reduced pressure to lower the boiling
point of the alkyltin trihalide, thereby reducing the amount
1~ of heat input required to isolate the product which is usually
obtained in yields of 90% or greater. The present method is
therefore limited to those alkyltin trihalides that boil below
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about 300C. under reduced pressures. Suitable alkyltin
trihalides contain between 1 and 5 carbon atoms and the
halogen is chlorine, bromine or iodine.
It is desirable to recover between about 50 and
100% of the total alkyltin trihalide by distillation. Any
remainder, together with the catalyst, is recycled by being
used as the diluent for a subsequent reaction.
The present method usually employs a stoichiometric
excesæ of alkyl halide relative to stannous halide. Preferably
this ratio is between 1.03 and 2.0 moles of alkyl halide for
every mole of stannous halide.
¦ The following non-limiting examples demonstrate
¦ preferred embodiments of the present method for preparing
I alkyltin trihalides. All parts and percentages are by weight
l unless otherwise indicated.
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¦ EXAMPLE 1
An autoclave was charged with molten monomethyltin
trichloride (1153g.; 4.80 moles) and anhydrous stannous
chloride (9lOg.; 9.79 moles). The autoclave was then sealed
and purged with methyl chloride to remove residual air, after
which it was cooled in dry ice and charged with trimethylamine
(16g.). The autoclave was then sealed and the contents heated
to 175-180!C. with agitation. Methyl chloride (440g.; 8.71
moles) was then pumped into the autoclave at a rate which
maintained a pressure of between 250 and 300 p.s.i.g.
Following completion of-the methyl chloride addition, the f
; mixture was stirred for 2 hours while being heated to 175-
180C. The total reaction time was about 6 hours. The
reaction mass was then cooled to about 60C. and transferred
to a distillation apparatus.
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¦ The distillate (1019g.), collected at 142-145C.
l (406-432 mm. of Hg.) was found to contain in excess of 90% by
¦ weight of monomethyltin trichloride.
¦ The residue (1219g.), consisting primarily of
¦ methyltin trichloride and catalyst, was transferred to the
autoclave for use in the reaction described in the following
example.
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EXAMPLE 2
The molten residue (1219g.) from the preceding
Example 1 and stannous chlorlde (9lOg.) were charged into an
autoclave, which was then purged with methyl chloride. No
additional catalyst was charged. The contents of the autoclave
were heated to 175-180C. The reaction and subsequent dis-
tillatlon were carried out as described in Example 1, yielding
a distillate (1081g.) and a residue (119Og.).
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EXAMPLE 3
The procedure of Example 2 was repeated using the
distillation residue (119Og.) of Example 2 as a solvent. No
addltional catalyst was used. The distillate weighed 1161g.
and the residue (1116g.) was suitable for recycling.
The combined distillates from Examples 1, 2 and 3
contained 97% monomethyltin trichloride, 2% dimethyltin
¦ dlchlor e, and 1% tin ( IV) chloride .
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EXAMPLE 4
An autoclave was charged with mineral oil (636g.),
triphenylphosphine (39g.; 0.149 mole), and stannous chloride
(lOOOg.; 5.27 mole). The autoclave was then sealed and the
air within the autoclave displaced by methyl chloride;
Agitation was continued while the contents Or the autoclave
were heated to 175-190C. Methyl chloride (372g.; 7.37 moles)
was then metered into the reactor pump at a rate that maintaine
a pressure of 250-300 p.s.i.g. within the reactor. After all
of the methyl chloride had been added the reaction mixture
was agltated while being heated to a temperature of 170-190C.
~ - ~or 4.5 hours, during which time the pressure remained
i relatively constant. The total reaction time was 9.5 hours.
The resultant mixture was cooled to about 148C. and then
dlstilled, yielding a nearly colorless distillate (1168g.)
boiling at 110-140C. (406-711 mm. of mercury). The distillat~
contained 97% methyltin trichloride and 3~ dimethyltin
dichloride. The distillatlon residue (732g.), consisting o~
mineral oil and catalyst plus associated methyltin halides,
was subsequently used to prepare additional methyltin
trichloride.
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EXAMPLE 5
; An autoclave was charged with methyltin trichloride
. (1153g.; 4.80 moles), stannous chloride (9lOg.; 4.79 moles),
and triphenylphosphine (69.7g.; 0.266 moles). The autoclave
was then sealed and the entrapped air displaced by methyl
chloride. The mixture was stirred and heated to between
175 and 190C. Methyl chloride (440g.; 8.71 moles) was then
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¦ metered into the autoclave at a rate which maintained the
pressure at between 250 and 300 p.s.i.g. The slight excess
of methyl chloride was required to maintain the pressure
l within the autoclave at 250-300 p.s.i.g. throughout the 4.5
¦ hour-long reaction period. After all of the methyl chloride
¦ had been added, the mixture was stirred for an additional 2
hours while the temperature was maintained between 175 and
l 190C. Approximately 50% of the resultant mixture was
¦ distilled at 142-145C. (406-432 mm. of mercury). The
¦ distillate (1019g.) was found to contain 98% methyltin tri-
chloride, 1.9% dimethyltin dichloride, and traces of tin (IV)
chloride. The residue (1350g.), containing the catalyst, was
¦ reused in a subsequent reaction.
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¦ EXAMPLE 6 . .
l The catalyst-containing residue (1325g.j of Example
¦ 5 and stannous chloride (9lOg.; 4.79 moles) was charged to an
autoclave. No additional catalyst was added. The mixture
was reacted with methyl chloride as described in Example 5,
and approximately 50% of the reaction mass was discilled.
The distill~te (1081g.) contained 97% methyltin
trichloride, 2.5% dimethyltin dichloride, and traces of tin
(IV) ch ride.
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